1. Field of the Invention
The present invention relates to a continuously-arranged sensor system for monitoring a state of an object to be detected, and also relates to a network unit and a sensor unit used for the continuously-arranged sensor system.
2. Description of the Background Art
In a manufacturing process in an automated manufacturing line, a process state of a workpiece is monitored in order to reliably process the workpiece. Therefore, in the automated manufacturing line, many sensors are arranged in proximity to the workpiece (object to be detected) so as to monitor the process state, and the workpiece is processed while a determination signal of each sensor is monitored.
In this kind of sensor system, it is cumbersome to prepare wirings between many sensors and a control apparatus of the sensors. Therefore, a continuously-arranged sensor system is known and utilized, in which these apparatuses are made into units and each unit is connected by physically coupling each unit, so that wirings between the units are completed at a time. In the continuously-arranged sensor system, many sensor units are continuously arranged in proximity to a workpiece, and many sensor heads such as optical fibers connected to each sensor unit are arranged in proximity to a portion of a workpiece to be monitored. In the continuously-arranged sensor system, a detection signal output from each sensor unit is monitored by a host control apparatus via a network unit.
Japanese Patent Application Laid-Open No. 2004-295276 describes a continuously-arranged sensor system for transmitting a sensor determination signal from each sensor unit to a network unit in real time, wherein two transmission paths, i.e., a parallel transmission and a serial transmission, are prepared as a method for transmitting other sensor information.
According to this configuration, since a sensor detection signal provided by each sensor unit is respectively independently transmitted via the parallel transmission path to the network unit side, the sensor detection signal can be transmitted to the network unit side without delay. Therefore, the workpiece can be operated at a fast speed. Further, a centralized control such as follows can be achieved: various kinds of sensor information such as the amount of received light and thresholds of sensors are transmitted to the network unit side as digital data, and a host control apparatus centrally manages the information. Alternatively, an instruction signal is transmitted from the host control apparatus or the network unit to each sensor unit so as to change controls and settings of light emitting timing of a sensor head in each sensor unit.
Japanese Patent Application Laid-Open No. 2003-97983 suggests a sensor system in which a plurality of sensor amplifiers and a sensor amplifier management apparatus are coupled via data communication.